With the recent increase in demand for data communication services, there have been introduced high-density, large-capacity optical fiber communication systems such as a polarization multiplexing method in which optical signals are multiplexed by means of optical carrier waves whose polarizations are orthogonal to each other, a digital coherent optical transmission method, and a super-channel method.
In the digital coherent optical transmission/reception method, the transmission rate can be increased by changing a multi-level degree of the modulation applying modulation methods such as BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), and 64QAM. In the super-channel method in which a plurality of subcarriers are multiplexed, the transmission rate can be increased by changing the number of subcarriers.
Here, in the super-channel method, in order to generate a plurality of subcarriers, it is required to provide as many components such as a light source, an optical modulation unit, and a digital coherent receiver as the subcarriers. The risk of failure occurrence increases with the number of the components increasing, and, if a failure occurs in a subcarrier in the super-channel optical signal transmission that is constituted by the plurality of subcarriers, the possible transmission capacity of the super-channel optical signal decreases by the capacity of the subcarrier in which the failure occurs, and it can become impossible to restore client signals to be accommodated in an optical transmitter/receiver.
To the problem that it becomes impossible to restore frames if a failure occurs at a part of lanes in multi-lane transfer, Patent Literature 1 discloses a multi-lane transfer system that performs a fallback in which a lane number subjected to the failure is excluded and performs protection using an unused lane. In the multi-lane transfer system, the fallback and the protection are performed by defining a region for a fault lane notification bit in an inserted multi-lane transfer function extension block and notifying from a receiver to a transmitter the lane number of a virtual lane subjected to a failure.